1. Field of the Invention
The present invention relates to a replenishing developer housing container and an image forming apparatus.
2. Description of the Related Art
In an electrophotographic image forming apparatus such as a copier or a printer, a surface of an image bearing member uniformly charged is exposed to light to thereby form a latent image thereon; the latent image is developed to form a toner image; and then the toner image is transferred onto a transfer material such as a recording sheet. The transfer material on which the toner image is borne passes through a fixing device, where the toner is fixed on the transfer material under the application of heat or pressure.
In the image forming apparatus, examples of a developing device for developing the latent image on the image bearing member includes a one-component developing device by means of a toner containing a magnetic material and a two-component developing device by means of a developer composed of a toner and a carrier.
Among them, the two-component developing device is excellent in developability, so that it is used in most of currently used image forming apparatuses. Particularly in recent years, color image forming apparatuses for forming full-color or multi-color images have been frequently used, and keen demand has arisen for the two-component developing device.
In the image forming apparatus including the two-component developing device, the toner and the carrier are stirred in the developing device, and the toner is frictionally charged with the carrier and electrostatically adheres to an outer surface of the carrier. The carrier bearing the toner is conveyed to a developing area, where the toner is released from the carrier under the application of a developing bias and electrostatically adheres to the latent image on the image bearing member to thereby form a toner image. Therefore, in order to provide an image satisfying high durability and high stability by the two-component developing device, it is essential that the toner is stably charged with carrier during stirring. That is, it is essential that the carrier has a stable charge-imparting capacity even after use for a long period of time.
However, in the typical two-component developing device, the toner is consumed as a developing operation proceeds, whereas the carrier is not consumed and remains in a developing tank. Therefore, the carrier to be stirred with the toner in the developing tank deteriorates by a peeling of a coating resin from a surface of the carrier or an adherence of the toner to the surface of the carrier as the frequency at which they are stirred together is increased. Accordingly, resistivity of the carrier and chargeability of the developer are gradually decreased, so that developability of the developer excessively increases. As a result, various failures such as an increased image density and foggy images are induced.
In order to solve the problem, Japanese Patent Application Publication (JP-B) No. 02-21591 discloses a trickle developing device in which a carrier is gradually replaced by adding the carrier at the same timing as the toner which is consumed upon developing. Thus, a charge amount is prevented from varying and an image density is stabilized.
A replenishing developer composed of a toner and a carrier is replenished from a replenishing developer housing container as is the case with only a toner. For example, there is proposed a toner housing container that includes a rotatable tubular powder housing member, a conveying pipe receiving member fixed to the powder housing member, an opening provided in the conveying pipe receiving member, and an uplifting portion configured to uplift the toner upward in the container along with rotation of the container body (e.g., see JP-B No. 02-21591). According to this proposed technique, the toner is uplifted by the uplifting portion along with rotation of the container body, and the toner falls from the uplifting portion during the rotation and is supplied into the conveying pipe.
However, in the case of a system that employs the mechanism of uplifting the toner by the uplifting portion and supplying the toner into the conveying pipe, there has been a problem that a developing device is difficult to be replenished with the toner when only a small amount of the toner remains in a toner bottle.
Accordingly, it is currently requested to provide a toner housing container being capable of replenishing a developing device with a toner even when only a small amount of the toner remains in a toner housing container.